(a) Technical Field
The present invention relates to a starting and generating system for a hybrid vehicle. More particularly, the present invention relates to a starting and generating system for a hybrid vehicle, which may copes with the requirement of a large-capacity motor, and solves a problem regarding a limitation in view of a layout when a single large-capacity motor is used, and a limitation in application of the large-capacity motor due to an increase in load applied to the shaft of the engine
(b) Background Art
In general, a hybrid vehicle, which is a vehicle that travels using an engine and a motor as driving sources, is an environmentally-friendly vehicle that travels using both energy generated from fossil fuel and electrical energy, thereby reducing exhaust gas and improving fuel efficiency.
FIG. 1 is a view illustrating a configuration of a powertrain of a hybrid vehicle according to the related art, which illustrates a configuration of a powertrain of a transmission-mounted-electric-device (TMED) type in which a drive motor and a transmission are attached. As illustrated in FIG. 1, the configuration of the powertrain of the hybrid vehicle includes an engine 1 and a drive motor 3 which are disposed in series as driving sources for driving a vehicle, an engine clutch 2 which is interposed between the engine 1 and the drive motor 3 to transmit or block power between the engine 1 and the drive motor 3, a transmission 4 which changes power from the engine 1 and the drive motor 3 and transmits the power to a driving shaft 5, and a starter-generator (e.g., integrated starter and generator (ISG) or hybrid starter and generator (HSG)) 6 which is connected with the engine 1 to transmit power.
Particularly, the engine clutch 2 is configured to transmit or block power between the engine 1 and the drive motor 3 while being engaged (lock-up) or disengaged (open). A battery 8, operating as a power source (e.g., electric power source) for the vehicle, is connected to the drive motor 3 and the starter-generator 6 via an inverter 7 to be charged and discharged, and the inverter 7 is configured to convert a direct current (DC) from the battery 8 into a three-phase alternating current (AC) and then apply the three-phase alternating current to the drive motor and the starter-generator to operate the drive motor 3 and the starter-generator 6.
Unlike a general vehicle with an internal combustion engine in which a starter motor and a generator are mounted separately, the starter-generator 6 is a device that performs an integrated function of a starter motor (starter) and a generator (alternator) in the hybrid vehicle. The starter-generator 6 is configured to start the engine 1 by transmitting power to the engine 1 through a belt 9 while being operated, or generate electric power using rotational force transmitted from the engine, and charge the battery 8 with electrical energy produced by the operation of generating electric power. In other words, the engine needs to be started when a mode is changed from an electric vehicle (EV) mode, which is a pure electric vehicle mode in which the hybrid vehicle travels by using power of the drive motor 3, to a hybrid electric vehicle (HEV) mode in which the hybrid vehicle travels using both power of the engine 1 and power of the drive motor 3, and in this case, the starter-generator 6 is used.
Since a pulley 6A of the starter-generator 6 is connected with a crank pulley 1A mounted to a crank shaft (C/S) of the engine 1 through the belt 9 to transmit power, the starter-generator 6 is operated as a motor and is configured to transmit rotational force to the crank shaft through the belt 9, to start the engine. When the engine is being operated, the starter-generator 6 is configured to receive rotational force of the engine 1, that is, rotational force of the crank shaft through the belt 9 and is operated as a generator to produce electrical energy and charge the battery 8.
When the vehicle is stopped (e.g., the vehicle brake is engaged), the starter-generator 6 is operated as a generator and produces electrical energy using rotational force transmitted from the engine 1 through the belt 9, and as a result, energy regeneration for charging the battery 8 is performed. The electrical energy, which is stored in the battery 8 as described above, is used to operate the drive motor 3 to drive the vehicle.
Hereinafter, in the present specification, a configuration, which includes the starter-generator for a hybrid vehicle and a power transmission mechanism that connects the starter-generator and the engine to transmit power between the starter-generator and the engine, is referred to as a starting and generating system for a hybrid vehicle. Meanwhile, the starting and generating system in the related art uses the power transmission mechanism that includes the belt and the pulley as described above, and adopts a power transmission method that connects the engine and the starter-generator with the belt.
However, the belt transmission method has a disadvantage in terms of controllability, and during battery charging for managing a level of a charged state of the battery, deterioration in transmission efficiency due to tension or a slip of the belt (e.g., the occurrence of slips and the like) may cause deterioration in overall efficiency of the vehicle. Particularly, since an operation range of the starter-generator is widened as the function of the starter-generator increases to not only a function of a starter motor for starting engine, but also a function of a series mode in which the starter-generator operates the engine and generates electric power using engine power to operate the drive motor using the electric power, a large-capacity motor is required to be used as the starter-generator.
In the case of a large-sized vehicle (e.g., a truck), an increase in size of the starter-generator and an increase in capacity of the motor are required, but there is difficulty in using a single motor of which the size is increased and coping with the requirement of the large-sized vehicle due to a limitation caused by an increase in lateral loads applied to various types of shafts of the engine and a limitation in terms of a layout of a belt system of the engine.
The above information disclosed in this section is merely for enhancement of understanding the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.